Nowaday, power generation using renewable energy sources, for example, photovoltaic power generation, wind energy power generation, fuel cell power generation, has been developed from power supplies having small power at early time to grid-connected power generation as public power at present, and are developing towards quantity production and large-scale utilization, and correspondingly the application range thereof has extended to various power utilization fields.
With the proliferation of power generation using renewable energy sources, grid-connected converters are increasingly upgraded. Taking a photovoltaic power generating system as an example, grid-connected converters have developed from transformers having low-frequency isolation originally to transformers having high-frequency isolation, and finally to omission of transformers.
An equivalent photovoltaic-panel-to-ground capacitance is relatively large, and thus, in consideration of leakage current in a system loop, if an input terminal is a photovoltaic input, then circuit topologies or control modes having low leakage current shall be selected. Accordingly, various converter circuit topologies such as H4, H5 and H6 (four-switch, five-switch and six-switch) or the like are derived. However, all of these converter circuit topologies have only considered a case where electronic outputs at an output port under a grid-connected operation and electronic outputs at an output port under a standalone operation are consistent, but none of them applies to a case where the requirements of the grid-connected operation and the standalone operation are inconsistent.
Taking a converter, which has a H6 topology and low leakage current in the photovoltaic grid-connected field, as an example, as shown in FIG. 1, during the grid-connected operation, the converter provides a single-phase two-wire output at an output port, and during the standalone operation, the converter can only provide the single-phase-two-wire output as well. Apparently, the converter does not apply to a scenario where the standalone operation requires a single-phase-three-wire output. In related arts, other converter circuit topologies also have the above problems.
Therefore, there exists a need to provide a power conversion device aiming at the above problems.